Air and other gasses often need to be cleaned. Solids need to be separated from a gas at times for use in industrial applications or possibly as food. Solids can also be separated to keep a solid material out of the environment.
Cyclone separators are used to separate material such as flour from air. The cyclones can be relatively efficient if the solids are somewhat dense.
Filters are widely employed for separating solids from a gas. Some of these filters catch and hold solids until the filter is partially plugged. The plugged filter is then removed and destroyed or cleaned. Other filters are partially cleaned by short periods of gas back flow.
Filters generally require a large surface area and substantial space. Operations of many filter systems require a system shut down for filter cleaning or replacement.
Gasses, that need to be cleaned, may be at elevated temperatures. Gasses at high temperatures may destroy filters, cooling before filtering can be expensive. Gas scrubbing and cooling with water applied directly to the dirty air may create a toxic sludge that is difficult to contain.